Process for recovering zirconium oxide



Patented Apr. 6, 1937 Henri- George; Paris, and Roger Lambert,Levallois-Perret, France, assignors to Societe Anonyme des Manufacturesdes Glaces & Produits Chimi'ques de' Saint- Gobain, Chauny & Cirey,Paris, France No Drawing.

Application November 27, 1934,

Serial- No.- 754,994.- In France December 23,

4 Claims.

This invention relates to a process of recovering' zirconia, i. e.zirconium oxide; from ores and minerals containing the same, such aszirconium silicate or zircon, and to products of such re- 5 covery; Thepresent application is a continuation-in-part of our copendin'g patentapplication Serial No. 702,964, filed December 18, 1933.

Zirconium principally occurs innature in the form of its silicates, suchas zircon", zirkite; etc;

10 In the past, considerable difiiculty has been experienced i'n'finding asatisfactory process for recovering zirconium oxide in asu-fiiciently pure state to enable it tobe exploited commercially.

In working up zirconium ores for the produc- 5 ti'on of zireonia it hasbeen found necessary, ac-

cording to one process, to first treat the ore with hydrofluoric acid toextract some of the silica. The purified zirconium silicate is thencalcined for about two hours at temperatures ranging be- 20 tween 1500-C. and- 1 600'C.

The calcined zirconium ore is thencomminuted by placing it in water andthe zirconia and silica, the combination between which has been brokenup incidental to the calcinationprocess, maythen 25 beseparated duetothe difierencein their specific gravity.

; This process is not altogether satisfactory becauseof-the fact thatthe zirconium oxide'or zir'- conia contains substantial amounts ofsilica as- 30 impurity; since the zirconium silicate will notbealtogether decomposed into zirconiaand silica even though thecalcination maybe extended for several hours.

According toanother method used heretofore,

35 minerals containing zirconium were heated with a mixture of achlorid' and, preferably; an oxide of an alkaline element.

The reaction mixture is pulverized and dissolved in-. sulphuric acidwhereupon thesilica is 40 left as an insoluble residuewhil'e thezirconia goes into solution. The solution of zirconium may be separatedfrom the insoluble silicic acid and thezirconium oxide may beprecipitated from such" solution.

45 This-method is-quite expensive and has to be continued for a verylong time.

An' object of the present invention is the provision of asimple andcheaperprocess of readily recovering pure zirconium oxide fromzirconiumsilicate.

Another" object is toprovide a process oi. preparing zirconiafromzirconium ores according to which zirconia and a silicate will be formedin such a; condition, or such intermixture, thatthey may be directlyutilized for abrasure, as an insu- 5 lator, and/ or as a refractorymaterial.

A further object of the present invention is the provision of aprocessof recovering pure zirconium oxide in comparatively largequantities with the use of acomparatively small amount of hydrofluoricacid.

The present invention isbased on the discovery that zirconium silicate,while being molten, decomposes-itself into zirconium oxide and silica.

Naturally, for the purposes of this invention it is necessary that theentire amount of zirconium silicate used inthe" process be decomposedinto zirconium oxide and silica.

In accordance with the presentinvention, substanceswhich will react withsilica without combining with zirconium oxid'e-are added to the mixtureof" zirconium oxide and silicawhich has been produced bythe-decomposition of zirconium silicate caused by fusion.

According t'oan embodiment of the present invention, zirconiumsilicateis first fused to decompose it intocrystalline zirconium oxideand silica. It is then allowed to cooli and is then ground orcomminute'd. Then hydrofluoric acid is added to-it. Thisacidwillreactwith the silica to-form volatile silicon fluoride (Si-F4). The zirconiumoxide in the condition in which it is formed from the fusion will not'react with hydrofluoric acid. The siliconfluoride can be easily andconveniently removed, leaving pure crystalline zirconium oxide. Theresult of this process is arapid and complete elimination of thesilica.

According to'another embodiment of the present invention certain metaloxides capable of forming insolublecrystalline silicates are added 40before fusion to thezir'conium" ore or zirconium silicate;- Among theoxides which may be added to the zirconium silicate-before-the' fusion,are aluminum oxide; calcium oxide and/or magnesium oxide. Other oxidesof the alkali earth or earth groups andsecond or third group of theperiodical tablemay also be" employed.

These alkali earth metal or earth metal oxides will react with the thefusedmi'xtureof silica, and zirconia resulting from decomposition 50.

of the zirconium ores or zirconium silicate, to form a silicate uponcooling, which silicate may be used for many purposes in intermixturewith the zirconia.

For example, the resulting product consisting of a mixture ofcrystalline zirconia with a crystalline silicate may be used as anabrasive, an electrical insulator, or a refractory material, dependingon the amount of zirconium oxide which it contains. It is entirelycrystalline and its small crystals are very compact. The product isparticularly adapted for use as a heat-proof or refractory material, forinstance for glass-manufacturing ovens or pots, since it is not subjectto deterioration when exposed to the action of molten glass.

By way of example, 82.5 parts by weight of bauxite containing 45%aluminum oxide and 40% silica, may be mixed with 17.5 parts by weight ofzirconium silicate and the mixture'is fusedfor example, in an electricalarc furnace. After the mixture has been allowed to cool rapidly, arefractory crystalline product is obtained which retains its structureup to a temperature of about 1720 C.

20 to 30 parts of zirconium silicate may be fused with 80 to 70 parts ofalumina to form an abrasive material which is harder than corundum, or acrystalline refractory material which retains its structure up to atemperature ranging between 1850 C. and 1780 C.

70 parts by weight of zirconium silicate may be fused with 30 parts ofaluminum oxide to form a crystalline product which can be usedconveniently as an electrical insulator and which has many excellentmechanical properties.

Zirconium oxide may be added to the fused mixture of zirconium silicateand aluminum, magnesium and/or calcium oxide to increase the amount ofzirconium oxide in the finished prodnot. On the other hand, silica maybe added to this mixture if it is desired to increase the amount of thesilicates in relation to the amount of zirconium oxide, in the finishedproduct.

According to a further embodiment of the present invention the mixtureof zirconium oxide and silica obtained by fusion is cooled, comminutedand then passed through a sieve. Then sodium carbonate is added and themixture is heated again to a temperature which should be lower than thatof fusion but which should be sufiiciently high to frit the mixture andto cause a formation of sodium silicate. This sodium silicate isdissolved and removed, and the solid residue containing all of thezirconium oxide and a certain amount of silica which has not reactedwith the sodium, is treated by the addition of hydrofluoric acid to theresidue.

In practice, this process may be carried out in the following manner:

A predetermined quantity of zircon is placed in an electrical furnaceand is fused there by a three-phase electrical are which usuallyrequired from 4 to 6 kilowatt-hours per kilogram of the molten product.On the average, the resulting molten substance contains 66% of zirconiumoxide, 29% of silica and of other substances.

The molten mixture is cooled and then ground or comminuted. Thecomminuted mixture is passed through a sieve.

Iron particles contained in the mixture after it has passed through thesieve, are removed by a magnet or by treating the mixture with dilutedsulphuric acid.

Then sodium carbonate is added tothe mixture in a proportion of 800grams of sodium carbonate to each kilogram of the comminuted mixture,and the mixture of sodium carbonate, zirconium oxide and silica isfritted by heating it for about one hour at a temperature rangingbetween 600 C. and 700 0., whereby a large portion of sodium carbonatereacts with the silica to form sodium silicate.

The fritted mixture is washed in water to remove the sodium silicate.

Finally, hydrofluoric acid, preferably in the form of a 10% to 60%solution, is added to the residue. The silica contained in the residuereacts with the hydrofluoric acid and forms volatile silicon fluoride.The remaining zirconium oxide is washed in slightly sulphurized water toremove all traces of iron and is finally washed in pure water.

By this process a very pure crystalline zirconium oxide is obtained.Only a small amount of hydroflouric acid is used up in the course ofthis process, since this acid merely completes the action of sodiumcarbonate. Experience has shown that sodium carbonate alone can neverremove the entire amount of the silica.

What is claimed is: V

1. The process of recovering zirconia from zirconium ores, whichcomprises fusing zirconium silicate until the entire zirconium silicateis decomposed into silica and crystalline zirconia, and

then removing the silica by treating the mixture in a cold state withhydrofluoric acid which reacts wth the silica without attackingcrystalline zirconia, whereby pure crystalline zirconia is recovered. I

2. The process of recovering zirconia from zirconium ores, whichcomprises fusing zirconium silicate until the entire zirconium silicateis decomposed into silica and crystalline zirconia, treating the mixturewith sodium carbonate at a temperature ranging between 600 C. and 700C., which at that temperature reacts with a portion of said silicawithout attacking zirconia, whereby a portion of said silica is removedand then treating the residue with hydrofluoric acid to remove the restof the silica, said hydrofluoric acid reacting with the remaining silicawithout attacking crystalline zirconia, whereby pure crystallinezirconia is recovered.

3. The process of recovering zirconia from zirconium ores, whichcomprises fusing zirconium silicate until the entire zirconium silicateis decomposed into silica and crystalline zirconia, cooling the mixtureof silica and crystalline zirconia, comminuting said mixture, heatingsaid mixture with sodium carbonate to a temperature ranging between 600C. and I00" C. which at that temperature reacts with a portion of saidsilica to form sodium silicate without attacking zirconia, removing saidsodium silicate, and then treating the residue with hydrofluoric acid toremove the rest of the silica, said hydrofluoric acid reacting with theremaining silica without attacking crystalline zirconia, whereby purecrystalline zirconia is recovered.

4. The process of recovering zirconia from zirconium ores, whichcomprises fusing zirconium silicateuntil the entire zirconium silicateis decomposed into silica and crystalline zirconia, cooling the mixtureof silica and crystalline zirconia, comminuting said mixture and passingit through a sieve, removing iron particles from said mixture, addingsodium carbonate to said mixture, fritting the mixture by heating thesame to a temperature ranging between 600 C. and 700 C said sodiumcarbonate at that temperature reacting with a portion of said silica toform sodium silicate without attacking zirconia, washing the frittedmixture to remove sodium silicate, treating the residue withhydrofluoric acid to remove the rest of the silica, said hydrofluoricacid reacting with the remaining silica without attacking crystallinezirconia, and removing traces of iron from said zirconia, whereby purecrystalline zirconia is recovered.

HENRI GEORGE. ROGER LAMBERT.

